In general, a polycarbonate resin to be produced from bisphenol A or the like is used in various applications because of its excellent transparency, heat resistance, and mechanical properties. However, the polycarbonate resin has disadvantages in that: in the case where the polycarbonate resin is used for applications such as blow molding, extrusion molding, and the like, a satisfactory molded product cannot be obtained because the polycarbonate resin has low melt tension; and in the case where a polycarbonate resin having a relatively low molecular weight is used for improving transferability etc. in injection molding and the like, a satisfactory molded product cannot be obtained because of stringiness and the like.
As a solution for these disadvantages, there is known a method using a branched polycarbonate resin prepared by adding a branching agent having three functional groups (see Patent Document 1, for example).
The branched polycarbonate resin obtained through this method assuredly has improved melt tension, moldability, and excellent physical properties, but the problem is that productivity is degraded because the organic phase containing a polymer and the aqueous phase containing by-products and the like have poor separability during a polymer solution washing step for polymer production. In particular, in the case where a method of adding a branching agent into an aqueous phase is employed or a branching agent hardly dissolving in an organic solvent is used, a semi-hydrophilic or semi-lipophilic polycarbonate oligomer accumulates in a state of a cream between an aqueous phase and an oil phase, to thereby cause problems such as inhibiting stable production, requiring a long separation time, and requiring a multi-step separation operation.    Patent Document 1: JP-A-03-182524